1. Field of the Invention
The present invention relates to a retainer for holding a printed circuit card between spaced surfaces and particularly to a retainer which facilitates entry and removal of a card from between those surfaces.
2. Background Information
As is well known to those skilled in the art, electronic equipment often employs printed circuit cards containing electrical circuitry. These cards are commonly mounted in a chassis or printed circuit card rack by stacking the cards in row alignment with one another. The row alignment is defined by slotted or spaced surfaces within or on the chassis, with each card placed between a pair of the spaced surfaces.
Printed circuit card retainers, for holding a printed circuit card between spaced surfaces, are known which comprise a partially threaded screw or a rod and three members slidably mounted end-to-end on the rod. The middle member has an internal longitudinal channel with a transverse dimension greater than the corresponding outside dimension of the rod to permit movement of the middle member along a transverse path relative the rod. The middle member and the adjacent end members have end portions which are engageable one another and shaped to force the middle member to move in a first direction along the transverse path relative the adjacent members upon forcing of the adjacent members toward the middle member.
To selectively force the adjacent end members toward the middle member, the rod of known prior art retainers comprises threads on one end and a shoulder on the other end. Recipient thread is provided on one of the end members to permit effective shortening of the rod upon rotation of the rod relative the one end member containing the recipient threads.
Prior art retainers of the type referred to above are designed to have a narrow width, when the middle member is not moved in the first direction along the transverse path, sufficient in size to permit insertion of the retainer and a card to which the retainer is mounted between the spaced surfaces on the chassis. Upon rotation of the rod and corresponding movement of the middle member in the first direction, the middle member engages one of the spaced surfaces and the card engages the other spaced surface and thereby holds the retainer and card between those spaced surfaces.
To remove the card from the chassis, the rod is rotated in a manner which relieves the forcing together of the adjacent members toward the middle member, thereby permitting the middle member to move in a direction opposite the first direction allowing the members of the retainer to assume a relaxed position and the card to be removed from between the spaced surfaces.
Although such prior art retainers are typically mounted on a printed circuit card, in the alternative the retainer could be mounted on one of the spaced surfaces, with the card inserted between the retainer and the other of the spaced surfaces. In addition, the middle member, in some prior art embodiments, actually comprises three or more members, arranged adjacent one another on the rod between the end members, with each of these "middle" members having end portions which are engageable to one another and shaped to expand the middle members, alternately, in a transverse path relative to the rod and the end members as the end members are forced toward the middle members.
Generally, space is at a premium where printed circuit cards are held. Therefore, the distance between stacked cards and the corresponding distance between spaced surfaces holding the cards must be designed to be an absolute minimum. The resultant available clearance between the spaced surfaces and the printed circuit card and retainer combination is therefore at a mimimum. Hence, when the members of a prior art retainer are in a relaxed position, insertion of the printed circuit card and retainer combination is hampered if the alignment of the members relative to one another is not maintained in an optimum position.
Misalignment of the members of a prior art retainer is caused by the individual members being able to rotate about the rod relative to one another when in the relaxed position. This results in some instances in the width of the retainer and card combination being greater than the distance between spaced surfaces. This discrepancy between the width of the retainer and card combination when in the relaxed position, and the distance between the spaced surfaces, results in the card not being freely insertable between the spaced surfaces, thereby causing excessive wear and tear on the retainer and card as a result of trying to force the retainer and card between the spaced surfaces.
Moreover, during shipping and handling of prior art retainers, individual members of such retainers are free to abrasively contact one another, thereby possibly damaging the finish on the members, resulting in rejection of otherwise useful retainers.
It is, accordingly, an object of the present invention to maintain the members of a printed circuit card retainer in a desired alignment relative one another when in the relaxed position during insertion and removal of a retainer and card combination between spaced surfaces, and during shipping and handling of the retainer.
Additional objects and advantages of the invention will be set forth in the description which follows and in part will be obvious from the description or may be learned by practice of the invention.